Method for checking a semiconductor switch for a fault

Abstract

The invention provides a method for checking a semiconductor switch for a fault, wherein the semiconductor switch is driven with a PWM signal with a variable duty cycle. To the benefit of determining faults on the semiconductor switch reliably and cost-effectively, it is provided that if the semiconductor switch is operated with a duty cycle of 100% or 0%, the current measurement of the overall system is evaluated, while if the semiconductor switch is operated with a duty cycle of between 0% and 100%, the generated voltage pulses across the semiconductor switch are evaluated.

The invention claimed is: 
     
       1. A method for checking a semiconductor switch for a fault, the method comprising:
 driving the semiconductor switch with a PWM signal with variable duty cycle, 
 wherein when the semiconductor switch is operating with a duty cycle of 100% or 0%, evaluating the current measurement of an overall system into which the semiconductor switch is integrated, 
 wherein while when the semiconductor switch is operating with a duty cycle between 0% and 100%, evaluating the voltage pulses generated across the semiconductor switch; 
 wherein the voltage pulses generated across the semiconductor switch are counted for the evaluation, and as a result of the evaluation a short circuit or an open circuit of the semiconductor switch is detected if the latter does not generate voltage pulses. 
 
     
     
       2. The method as claimed in  claim 1 , wherein at a duty cycle of 100% or 0% the evaluation is aborted and a fault is determined via the current measurement of the overall system. 
     
     
       3. A device for carrying out a method for checking a semiconductor switch for a fault, the method comprising:
 driving the semiconductor switch with a PWM signal with variable duty cycle, 
 wherein when the semiconductor switch is operating with a duty cycle of 100% or 0%, evaluating the current measurement of an overall system into which the semiconductor switch is integrated, 
 wherein while when the semiconductor switch is operating with a duty cycle between 0% and 100%, evaluating the voltage pulses generated across the semiconductor switch; and 
 wherein the voltage pulses generated across the semiconductor switch (S 3 ) are tapped off it via a capacitor (C 4 ) and applied to an A/D converter (Q 1 , Q 2 ), which applies a digital signal (Timer) to the counter input of a controller for the evaluation. 
 
     
     
       4. The device as claimed in  claim 3 , wherein the voltage pulses tapped off by the capacitor are converted by a diode (D 4 ) into positive pulses that are applied to the A/D converter (Q 1 , Q 2 ). 
     
     
       5. The device as claimed in  claim 3 , wherein the voltage pulses generated across the semiconductor switch are counted for the evaluation, and as a result of the evaluation a short circuit or an open circuit of the semiconductor switch is detected if the latter does not generate voltage pulses. 
     
     
       6. The device as claimed in  claim 3 , wherein the voltage pulses generated across the semiconductor switch are counted for the evaluation, and as a result of the evaluation a short circuit or an open circuit of the semiconductor switch is detected if the latter does not generate voltage pulses, and
 wherein at a duty cycle of 100% or 0% the evaluation is aborted and a fault is determined via the current measurement of the overall system.